[NEIGH]: Convert neighbour deletion to new netlink api

Fixes:
  Return ENOENT if the neighbour is not found (was EINVAL)
  Return EAFNOSUPPORT if no table matches the specified
  address family.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>